Dual rail network for a remote switching unit

ABSTRACT

A time-space-time switching network (for local to local traffic), a time-space or a space-time switching network portion (for local to remote traffic) is shown for a small remotely located switching system. There are multiple crossovers of PCM data from one information rail to another information rail in this switching system. These two information rails provide for crossover in both the originating and terminating time switching stages for local calls and in only the originating or terminating time switching stages for calls originating or terminating at remotely located switching systems. The information rails remain segregated through the space switching stage of this switching system. The small remotely located switching system is connected to a large host digital switching system via digital spans.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is related to U.S. Pat. Nos. 548,481; 548,482; and 548,484, having the same inventive entity and being assigned to the same assignee as the present application.

BACKGROUND OF THE INVENTION

The present invention pertains to digital communication switching systems and more particularly to an enlarged capacity remotely located switching system which interconnects large central office systems to local subscribers or other smaller remotely located switching systems.

The networks of large modern day switching systems typically employ solid state digital time division switching techniques. An ever increasing number of telephone subscribers has provided for an increasing requirement for central office switching system capability. As population growth expands outward from large metropolitan areas, these growth areas require modern day telephone service. To meet this need and to provide for interfacing with the large digital switching systems, smaller remotely located digital switching systems are required.

In order for the smaller digital switching systems to operate efficiently, they must provide the capability of easily interfacing with their larger counterparts. These smaller switching systems provide for handling between a few hundred and a few thousand telephone subscribers. To provide effective, efficient and economical service to such a number of subscribers, a switching system must be tailored to serve a particular number of subscribers. Large time division switching systems may be able to fill the requirement of handling telephone subscriber traffic; however, they are inefficient and uneconomical because much of their capacity is unused.

One such switching system is a non-folded T-S-T modular network taught by U.S. Pat. No. 3,956,593, issued to A. A. Collins et al., on May 11, 1976.

Another large time-space-time switching network is taught in U.S. Pat No. 4,005,272, issued on Jan. 25, 1977, to A. A. Collins et al. Both of the above mentioned switching systems exhibit the problem that they would be uneconomical in applications of small remote unit switches as mentioned above.

Another large switching system is taught by U.S. Pat. Nos. 4,406,005; 4,399,369; 4,399,533; 4,399,534; 4,392,223; and 4,402,077, all issued to N. Simmons during 1983 and assigned to the same assignee as the present invention. These patents depict the switching network of the base unit of the GTD-5 EAX switching system. Again, use of these units would be uneconomical to provide service for up to a few thousand subscribers.

Accordingly, it is the object of the present invention to provide an effective, efficient and economical digital switching network for a remotely located switching system handling between a few hundred to a few thousand telephone subscribers.

SUMMARY OF THE INVENTION

In a remote switching arrangement, a remote switching unit is connected between subscribers and other switching systems via interface equipment. The remote switching unit comprises two PCM buses connected to the subscribers and to the other switching systems via the interface equipment. These PCM buses transmit the plurality of PCM data samples. First and second originating time switches are connected to the interface equipment via these two PCM buses. These originating time switches are operated to switch PCM samples transmitted from the interface equipment.

The originating time switches each include first and second memories which are connected to the PCM buses. The first and second memories are also interconnected so that the first memory and second memory are written simultaneously in corresponding time slots with the transmitted PCM samples. The first and second memories are operated so that PCM samples transmitted on the first PCM bus may be switched to the second PCM bus for subsequent retransmission or so that PCM samples transmitted on the second PCM bus may be switched to the first bus for subsequent retransmission.

The remote switching unit also includes first and second space switches. Each of the space switches include a first set of latches connected to the first and second originating time switches. This set of latches is operated in response to the transmitted PCM samples to store the samples during each time slot. A multiplexer is connected to the first set of latches and is operated to transmit the stored PCM samples during each time slot in response to operating signals of a first predefined value. The first and second space switches also include a second set of latches connected to the multiplexer. These latches are operated to store PCM samples transmitted through the multiplexing arrangement during each time slot.

The remote switching unit also includes first and second terminating time switches which are connected respectively between the first and second space switches and the interface equipment. The first and second terminating time switches are operated to switch the PCM samples from the first and second space switches to the interface equipment for transmission to the subscribers.

The terminating time switches each include first and second memories which are connected between the second set of latches and the interface equipment. These memories are interconnected so that they are written into simultaneously and corresponding time slots for storing the PCM samples contained in the second set of latches. These memories are also capable of being operated to switch PCM samples from the first space switch through the second terminating time switch to the subscribers. These memories are also capable of being operated to switch PCM samples from the second space switch through the first terminating time switch to the subscribers.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of configurations of switching units of the switching system of the present invention.

FIG. 2 is a block diagram of the remote switching unit of FIG. 1.

FIG. 3 is a block diagram of the network portion of the remote switching unit of FIG. 2.

FIG. 3A is a schematic diagram of the originating time stage of the remote switching unit of FIG. 2.

FIG. 3B is a schematic diagram of the terminating time stage of the remote switching unit of FIG. 2.

FIG. 4A is a schematic diagram of a portion of the space switch rail A and control A and B as shown in FIG. 3.

FIG. 4B is a schematic diagram of another portion of the space switch rail A and control A and B of FIG. 3. FIGS. 4A and 4B taken collectively from the space switch rail A and control A and B as shown in FIG. 3.

FIG. 4C is a schematic diagram of the space switch rail B of FIG. 3.

FIG. 5 is a timing diagram of required signals for the space switches of the remote switching unit.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. 1, the GTD-5 EAX system is shown. The GTD-5 EAX is designed and manufactured by GTE Automatic Electric Incorporated. The GTD-5 EAX system is a family of stored program control telephone digital switching units intended to provide class 5 and class 4/5 switching service, spanning office sizes between 500 and 150,000 lines. The base unit of the GTD-5 EAX provides for interfacing the three other types of remote units to the telephone network.

These remote units are a remote switching unit (RSU), a remote line unit (RLU) and a multiplexer unit (MXU). The base unit (BU) is provided in two versions, a large base unit (LBU) and a small base unit (SBU). The LBU has a capacity of between 2,000 to 150,000 lines providing up to 360,000 call attempts per hour and 300,000 directory numbers. The LBU hosts all three types of remote units which are interconnected via digital facilities, such as T1 spans.

The SBU has identical features to the LBU with the exception that class 4C operation is not provided. Its capacity is in the range of 500 to 20,000 lines and provides for 65,000 call attempts per hour and up to 40,000 directory numbers.

The RSU is a small switching system designed to serve outlying communities of up to 3,000 lines. Although the RSU is controlled by the BU, it provides local to local switching service. The RSU is interconnected to the base unit via between 2 to 32 digital links, such as T1 spans. An RSU also provides the capability of hosting RLUs or MXUs. When interconnected by specific links, two co-located RSUs will function as an integral unit, thus extending service up to 6,000 lines.

The RLU is a concentrating pair gain unit serving up to 768 lines. The RLU interconnects to the host unit via between 2 to 8 digital links.

The MXU is a concentrating or a non-concentrating pair gain unit serving up to 96 lines. It is designed for either pedestal or pad mounting in the outside plant and it interconnects to the host unit via between 1 to 4 digital links.

Shown in FIG. 2 is a block diagram of the remote switching unit (RSU). The RSU is divided into two portions--a network portion and a processor portion.

Analog line facility interface units (FIU) and digital trunk FIUs interface the RSU to subscribers or to other switching units, respectively.

Each of the analog FIUs convert the incoming analog voice signals to PCM signals for transmission through the network. The sampling rate of an FIU is 8,000 samples per second or 1 sample every 125 microseconds. The analog FIU has a capacity of 193 channels. Each time frame is 125 microseconds in duration and there are 193 time slots per time frame. One FIU time slot is 648 nanoseconds in duration.

The network of the RSU is 12 bits wide. Each PCM sample comprises 8 bits of these 12 bits and includes 7 bits designating the magnitude of the signal and 1 bit indicating the sign of the signal. Three of the remaining 4 bits are for supervisory functions with the remaining bit being an odd parity bit over the entire 12 bit sample.

Each FIU provides for transmitting 193 channels of information to the network portion of the RSU. Two groups of 193 channels comprise an information rail. Therefore, each rail contains 386 channels of information.

The RSU serves up to a maximum of 8 FIUs (1 through 8) of which 4 FIUs (5-8) are dedicated solely to the base unit interface as shown in FIG. 2. The remaining 4 FIUs (1-4) may be a mix of analog line FIUs and digital trunk FIUs in any combination. The analog line FIU serves local subscribers connected to the RSU, whereas the digital trunk FIU may serve either RLUs or MXUs.

FIUs 1-4 are connected to the originating time stage 10 and to the terminating time stage 15 of the network portion of the RSU. Digital tone source 11 provides tones, such as busy and ringing tone to the subscribers via the originating time stage 10 and the terminating time stage 15. Remote clock 12 provides for detecting timing from the digital span interfaces connected between the RSU and the BU, and for distributing these timing signals to the originating time stage 10, the terminating time stage 15, and the local base link switch 13. The local base link switch 13 is connected to the originating time stage 10, the terminating stage 15 and to the digital trunk FIUs 5 through 8 which are in turn connected to the BU.

Cable driver/receiver 14 is connected to local base link switch 13 and provides for interfacing co-located remote switching units.

Local RSU traffic is transmitted via an analog line unit FIU, such as FIU 1, to the originating time stage 10, through the local base link switch 13, through terminating time stage 15 to an analog line FIU, such as FIU 1.

Local to base unit traffic is transmitted from analog line FIU 1 through originating time stage 10, through the local base link switch 13, to a digital trunk FIU, such as FIU 5, to the BU. Base unit to local traffic takes a path through a digital trunk FIU, such as FIU 8, to the local base link switch 13, through the terminating time stage 15 to an analog line unit, such as FIU 1. Remote line units and multiplexers may transmit telephone traffic to the base unit in a similar fashion to that mentioned above for local to base unit and base unit to local traffic. The RLU and MXU are connected to the RSU via a digital trunk FIU, such as FIU 4.

The heart of the processor portion of the RSU is processor 25. Processor 25 is a microprocessor which may be implemented with an Intel 8086 mioroprocessor device. Intel is a registered trademark of the Intel Corporation. Processor 25, along with memory 27, performs the logical analysis and sequencing of calls through the network portion of the RSU. In addition, processor 25 performs administrative and maintenance functions for the RSU.

A network bus interface 26 connects processor 25 to the network portion of the RSU.

FIU interfaces 20-24 and 30-34 permit processor 25 to control the operation of facility interface units 1-4 and 5-8, respectively. Co-located RSU interface 28 provides processor 25 with the ability to control co-located remote switching unit operation.

Referring to FIG. 3, FIUs 1 and 2 are connected to information memory originating (IMO) 51 and to IMO 57. Information memory originating 51 and 57 collectively comprise an originating time switching stage. FIUs 3 and 4 are connected to information memory terminating 52 and 58. Information memories 52 and 58 collectively comprise a terminating time switching stage. Control memory A and B 53 is connected to the RSU processor and contains switching information for controlling each of the information memories 51, 52, 57 and 58. Each FIU provides for transmitting 193 channels of information to the memory to which it is connected. Two FIUs, or two groups of 193 channels, comprise an information rail. That is, each rail contains 386 channels of information. Each information memory is capable of handling two such rails.

Each information memory is connected to its respective space switch rail A 55 or rail B 56. Space switches 55 and 56 constitute the local base link switch 13 of FIG. 2. Each information memory contains PCM samples representing the amplitude of a voice signal. Twelve bits are required. Eight bits represent the amplitude of the voice signal; three bits are supervisory information; and, one bit is parity. Since each information memory contains two rails of incoming or outgoing information, at least two physical memory units of 386 words are required.

PCM data is transmitted from a local line, an RLU, or an MXU through an FIU, such as FIU 1 through 4, and stored in information IMOA 51 or IMOB 57. The PCM data is then transmitted through space switch 55 for rail A or space switch 56 for rail B.

Next, the data is transmitted from space switch 55 or 56 to IMTA 58 or IMTB 52 where it is stored. At the appropriate time, control memory A and B 53 is written into by a processor of the RSU with the instructions indicating on which time slot the stored PCM sample is to be transmitted outward to one of the FIUs 1 through 4. The FIUs then transmit the PCM sample to either a local line, an RLU or an MXU.

For PCM samples transmitted to the RSU from the base unit, no originating time switching stage is required since these PCM samples have been time switched by the base unit. PCM samples from the base unit are transmitted and received by FIUs 5 through 8. These FIUs are connected to the base unit by digital spans. FIUs 5 and 6 are connected to space switch 55 and FIUs 7 and 8 are connected to space switch 56 and provide for transmitting the received PCM samples from the base unit into the switching network of the RSU.

Space switches 55 and 56 operate to transmit data in one of two directions. The space switches may transmit data from the IMOA 51 or IMOB 57 to the base unit via FIUs 5 through 8 or the space switches may transmit data received from the base unit via FIUs 5 through 8 to IMTA 58 or IMTB 52. PCM information transmitted to IMTA 58 or IMTB 52 will subsequently be transmitted via one of FIUs 1 through 4 to either a local line, an RLU or an MXU.

Information may be transmitted to the RSU from another co-located RSU. This information is received or transmitted by the extended driver/receiver time (EDRT) 59. Information received by the EDRT is transmitted to either space switch 55 or space switch 56. This PCM information is then either transmitted to the appropriate information memory terminating for transmission to a local line, RLU or MXU.

Referring now to FIG. 3A, a schematic diagram of the information memory originating IMOA 51 and IMOB 57 of FIG. 3 is shown. IMOA 51 and IMOB 57 comprise four information memory spaces, that is, information memory originating AA, AB, BA, and BB. A twelve-bit wide bus connects each FIU to each of two information memory originating spaces. FIUs 1 and 2 are connected via this bus through multiplexer 90, which is also twelve bits wide, to information memory originating AA and to information memory originating BA. FIUs 3 and 4 are connected via a twelve-bit wide bus and twelve-bit wide multiplexer 91 to information memory originating AB and information memory originating BB. The collection of 193 channels of FIUs 1 and 2 comprises rail A. Rail B is made up of 193 channels from FIUs 3 and 4. The information memory originating space identification space consists of two alphabetic letters. The first letter indicates the logical group of the memory and the second letter indicates the incoming rail from which the memory is written. As mentioned above, rail A is connected to information memory originating spaces AA and BA; while rail B is connected to information memory originating spaces AB and BB. Multiplexers 90 allow for the sharing of rail A by FIUs 1 and 2 and multiplexers 91 similarly allow the sharing of rail B by FIUs 3 and 4.

The rail A out bus connects information memory originating spaces AA and AB to the rail A portion of the space switch 55. Similarly, the rail B out bus connects information memory originating BA and BB to the rail B portion of the space switch 56. PCM samples received from FIUs 1 and 2 on rail A are simultaneously written into memories AA and BA and similarly, the PCM samples of rail B from FIUs 3 and 4 are simultaneously read into memories AB and BB. As a result, one memory space in each logical group contains the PCM information for each channel. Therefore, the PCM information may be transmitted through the space switch from either of the memories which contain the information, but only from one of these memories.

PCM information entering the originating time switch on rail A may exit on rail B and vice-versa. This information is then transmitted through the corresponding space switch on the corresponding rail to which it entered the space switch, since the space switches have their rails segregated. Similarly, information originating on rail B may be transmitted out of the originating time stage on the rail A out bus to rail A of the space switch.

This crossover of information from rail A to rail B and vice-versa is a substantial factor in allowing the size of the space switch to be minimal and prevents network blocking. Crossover in the space switch would require four times the switching capacity as the present space switch. As a result, this crossover configuration in the originating and terminating time switches provides for allocation of network paths equally through rail A and rail B.

Now referring to FIG. 3B, a schematic diagram of the information memory terminating as indicated by blocks IMTA 58 and IMTB 52 of FIG. 3 is shown. Similar to the information memory originating, the information memory terminating also comprises four information memory (terminating time switching stage) spaces AA, AB, BA, and BB. The rail A in and rail B in buses connect the respective space switches 55 and 56 of FIG. 3 to the information memory spaces of the terminating time stage. Rail A in and rail B in buses each contain 386 channels of PCM information.

The information memory terminating space is identified similar to that of the information memory originating space. The first letter of the designation indicates logical group of the memory and the second letter indicates the incoming rail from which the memory space is written. Rail A is connected to information memory terminating spaces AA and BA. Similarly, rail B is connected to information memory terminating spaces AB and BB.

The twelve-bit wide rail A out bus connects information memory terminating AA and AB to FIUs 1 and 2 through digital pad A and demultiplexers 95, which is also twelve bits wide. Similarly, the rail B out bus connects information memory terminating BA and BB to FIUs 3 and 4 via digital pad B and demultiplexers 94, which is twelve bits wide. Digital pads A and B permit input signals to pass directly through or to provide selective attenuation for the amplitude of these digital signals.

The voice samples transmitted on rail A are simultaneously written into information memories AA and BA. Similarly, PCM samples of rail B are simultaneously written into information memories AB and BB. As a result, one memory unit in each logical group contains the voice information for each channel. Information entering the terminating time switching stage on rail A may exit the terminating time switching stage on rail B and vice-versa.

Referring to FIGS. 4A and 4B collectively, these figures depict a block diagram of space switch rail A and control A and B 55 of FIG. 3. The rail A space switch 55 of FIG. 3 provides the control function for both space switches 55 and 56 as shown in FIG. 3. FIG. 4A is the network portion of space switch rail A and FIG. 4B is the control portion for both the rail A and rail B space switches 55 and 56.

PCM data on rail A of the RSU network is directed by 4:1 multiplexer 101 between the originating time switching stage and the terminating time switching stage of the RSU. Depending on the two-bit address of control leads CMA0 and CMA1 which are transmitted to multiplexer 101 for each time slot, the multiplexer 101 selects PCM data from one of its four inputs and transmits the data to the terminating time stage. This PCM data is then stored in both copies of information memory terminating, as outlined above. One input to multiplexer 101 is transmitted by flip-flop array 102. Flip-flop array 102 is connected to FIUs 5 and 6 through 2:1 multiplexer 103. The buses connecting each of the components mentioned above are twelve bits in width. Eight bits of these twelve are a PCM voice sample which includes a sign bit, three supervision bits and one odd parity bit. When the TSE lead, which connects multiplexer 103 to the clock, is low (this lead is low on each odd time slot) PCM data from FIU 5 is enabled to be transmitted to the input of multiplexer 101 via flip-flop array 102. When the signal on the TSE lead is high (it is high on all even time slots), PCM data from FIU 6 is enabled to be transmitted to the input of multiplexer 101 via flip-flop array 102. The inverted output signals of multiplexer 103 are latched by flip-flop array 102 on the rising edge of a clock signal on the ST0 lead. When the value of both the CMA0 and CMA1 leads is low, the data latched by flip-flop array 102 is enabled to the output of multiplexer 101. The clock signal on the ST2 lead enables flip-flop array 104 to latch the PCM data output by multiplexer 101. This latched data is then read out of flip-flop array 104 and transmitted to both copies of the information memory terminating of the terminating time switching stage.

A second input to multiplexer 101 is connected to quiet code generator 105. Quiet code is provided for any unused time slots so as to eliminate any PCM line distortion. Quiet code consists of a twelve-bit PCM sample, nine of which are at logic 1 and three of which are at logic 0. This provides an odd parity over the twelve bits which will inhibit the generation of any parity alarms. When the signals on leads CMA0 and CMA1 are respectively at logic 1 and logic 0, the quiet code generator output is gated through multiplexer 101 and latched by flip-flop array 104.

The next input to multiplexer 101 contains PCM data from local RSU subscribers. This PCM data is transmitted from the originating time switching stage of the RSU through flip-flop array 106 to multiplexer 101. The buses connecting the information memory originating to flip-flop array 106 and flip-flop array 106 to multiplexer 101 are also twelve bits in width.

During a particular time slot, if the PCM data latched in flip-flop array 106 is destined for another local RSU subscriber, then the signals on leads CMA0 and CMA1 will be at logic 0 and logic 1 respectively. As a result, multiplexer 101 will enable the contents of flip-flop array 106 to be gated through and latched by flip-flop array 104.

The PCM data latched in flip-flop array 106 is also latched in either flip-flop array 107 or flip-flop array 108. If the signal on the TSE lead is at logic 1 then flip-flop array 107 latches the PCM data. If the signal on TSE lead is at logic 0 then flip-flop array 108 latches the PCM data. Flip-flop array 107 is connected to FIU 5, while flip-flop array 108 is connected to FIU 6. In this manner, the PCM data is segregated for transmission on the even or odd time slots to the base unit. PCM data may be transmitted from a co-located RSU through flip-flop array 109 to multiplexer 101. Flip-flop array 109 latches the twelve-bit wide PCM data. When the signals on both the CMA0 and CMA1 leads are at logic 1, multiplexer 101 operates to gate the PCM data from the co-located RSU through to be latched in flip-flop array 104. This data is then written into the memory of the terminating time switching stage.

Parity checking is performed at two locations in each rail of the network portion of the space switch. First, the output of multiplexer 101 is also transmitted via a twelve-bit wide bus to parity check circuit 110. Parity check circuit 110 is a commercially available unit which is twelve bits wide and which checks for odd parity over the twelve bits. If bad parity is detected, parity check circuit 110 provides a logic 0 output and also latches the PCM data. The PBR lead will go low when bad parity is detected, thereby indicating bad parity on PCM data which is being transmitted to a local RSU subscriber.

Parity is also checked on PCM data transmitted from local RSU subscribers. When PCM data is latched by flip-flop array 106, parity check circuit 111 is operated on the P2 phase of the clock and examines the twelve bits latched by flip-flop array 106. If bad parity is detected, the signal on the PRB lead has the value logic 0, indicating that bad parity has been detected on a PCM data sample transmitted from the originating time switching stage.

The processor is connected to the space switching stage via the twelve-bit address bus CADD and the eight-bit bi-directional data bus. The CAD bus along with the time slot counter bus TSC is connected to multiplexer 121. When the clock lead P2 is at logic 1, the CADD bus is gated through multiplexer 121 and enabled to select an address for memories 122 through 125. During this period, one of memory units 122 through 125 is enabled. This is accomplished by the control decode circuit 130 utilizing the P2 signal and one bit of the address bus CADD (bit 10) to derive the SELA and SELE signals. Bit 9 of the CADD bus selects a particular address within the selected memory. Read/Write control is determined by bit 11 of the CADD bus, that is, logic 0 for a write and logic 1 for a read.

The memory units 122 through 125 are written with the proper information to ensure that multiplexer 101 is operated to gate the proper input through to the terminating time stage during each time slot. During the P0 portion of the network time clock, the memory units 122 through 125 are accessed by the time slot counter leads TSC. The information written into memory units 122 through 125 is then read out upon the occurrence of clock signal ST0. The result is latched in flip-flop array 132 for the rail A space switch and in flip-flop array 134 for the rail B space switch. The signals latched in flip-flop arrays 132 and 134 contain the information required to operate multiplexer 101. That is, the signals are the CMA0 and CMA1 leads required to operate multiplexer 101 to gate the appropriate input through to the terminating time stage as outlined above. Flip-flop array 134 contains the CMB0 and CMBl leads required to operate the corresponding multiplexer 201 in the rail B space switch.

Flip-flop arrays 133 and 135 permit the stored multiplexer control information to be read back via the eight-bit bi-directional data bus to the processor.

Parity check circuits 143 and 144 respectively check for odd parity over the time slot counter TSC bus and the processor address bus CADD. If bad parity is detected by parity check circuits 143 or 144, a logic 0 signal is provided on the PTSC or PAD leads respectively. Parity is also checked over the buses which operate multiplexer 101 and the corresponding multiplexer 201 in the rail B space switch. Parity check circuits 141 and 142 operat to check these two buses respectively. If bad parity is detected, a logic 0 signal is generated on the PMA lead by parity check circuit 141 or on the PMB lead by parity check circuit 142.

All of the above mentioned parity check circuits search for odd parity. If even parity is detected, the parity check circuit latches and remains set until reset by the processor. All parity alarm signals are ORed by AND gate 150 which transmits a master alarm signal to the processor. The processor may then address the alarm read logic 151 via the BLSFPE and BLSFPO leads and read the status of each of the parity alarms via the eight-bit bi-directional data bus via alarm read logic 151. In addition, the processor may set the alarm latches individually via the alarm set decode 152 utilizing the eight-bit bi-directional bus. In this way, the processor may detect a stuck or a not settable alarm latch in the alarm read logic 151.

Referring to FIG. 4C, a block diagram of the space switch rail B 56 of FIG. 3 is depicted. This diagram is the network portion of the rail B space switch. The logic shown in FIG. 4B provides the control function for the rail B space switch.

PCM data on rail B of the RSU network is directed by 4:1 multiplexer 201 between the originating time switching stage and the terminating time switching stage of the RSU. Depending upon the two-bit address of control leads CMB0 and CMB1 transmitted by flip-flop array 134 of FIG. 4B, multiplexer 201 selects PCM data from one of its four inputs and transmits the data to the terminating time switching stage via a flip-flop array 204. That is, the values for signals CMB0 and CMBl are transmitted to multiplexer 201 for each time slot.

Multiplexer 201 is connected to flip-flop array 202 and constitutes one input to multiplexer 201. Flip-flop array 202 is connected to FIUs 7 and 8 via 2:1 multiplexer 203. Multiplexer 203 is also connected to flip-flop arra 202. The buses which connect each of the above mentioned components are twelve bits in width. When the TSE lead, which connects multiplexer 203 to the clock, is low (this lead is low on each odd time slot), PCM data from FIU 7 is enabled to be transmitted through multiplexer 203 and latched by flip-flop array 202, so that, the latched values of flip-flop array 202 are available at the input of multiplexer 201. When the signal on the TSE lead is high (it is high on all even time slots), PCM data from FIU 8 is enabled to be transmitted through multiplexer 203 and be latched by flip-flop array 202, so that, the PCM data is available at the input to multiplexer 201. The inverted output signals of multiplexer 203 are latched by flip-flop array 202 on the rising edge of a clock signal on the ST0 lead. When the value of both the CMB0 and CMB1 leads is low, the data latched by flip-flop array 202 is enabled through multiplexer 201 to its output. When clock signal ST2 is low, flip-flop array 204 is enabled to latch the PCM data output by multiplexer 201. This latched PCM data is then read out of flip-flop array 204 and transmitted to both copies of the information memory terminating of the terminating time switching stage.

Multiplexer 201 is connected to a second input source, quiet code generator 205. Quiet code is provided for any unused time slots so as to eliminate any PCM line distortion. Quiet code consists of a twelve-bit PCM sample, nine bits of which are at logic 1 and three bits of which are logic 0. This provides an odd parity over the twelve bits, which will inhibit the generation of any parity alarms. When the signals on leads CMB0 and CMB1 are respectively at logic 1 and logic 0, the quiet code generator 205 has its output gated through multiplexer 201 and is latched by flip-flop array 204.

The next input to multiplexer 201 constitutes PCM data from local RSU subscribers. Flip-flop array 206 is connected between multiplexer 201 and the originating time stage. This PCM data is transmitted from the originating time switching stage of the RSU through flip-flop array 206 to multiplexer 201. The buses connecting the information memory originating to flip-flop 206 and connecting flip-flop 206 to multiplexer 201 are twelve bits in width.

During a particular time slot, if the PCM data latch by flip-flop array 206 is destined for another local RSU subscriber, then the signals on leads CMB0 and CMB1 will be at logic 0 and logic 1 respectively. As a result, multiplexer 201 will enable contents of flip-flop array 206 to be gated through and latched by flip-flop array 204.

The PCM data latched in flip-flop array 206 is also latched in either flip-flop array 207 or flip-flop array 208. If the signal on the TSE lead is at logic 1, then flip-flop array 207 latches the PCM data, which is subsequently transmitted to FIU 7. If the signal on the TSE lead is at logic 0 then flip-flop array 208 latches the PCM data which is subsequently transmitted to FIU 8. Flip-flop array 207 is connected to FIU 7, while flip-flop array 208 is connected to FIU 8. In this manner, the PCM data is segregated for transmission on the even or odd time slots to the base unit.

PCM data may be transmitted from a co-located RSU through flip-flop array 209 to multiplexer 201. Flip-flop array 209, which is connected between the originating time stage and multiplexer 201, latches the twelve-bit wide PCM data. When the signals on both the CMB0 and CMB1 leads are at logic 1, multiplexer 201 operates to gate the PCM data from the co-located RSU through to be latched in flip-flop array 204. This data is then written into the information memory terminating of the terminating time stage as outlined above.

Multiplexer 201 is connected to parity check circuit 210 and parity check circuit 210 receives the PCM data which is being transmitted to the terminating time stage. The bus connecting multiplexer 201 to parity check circuit 210 is twelve bits wide. Parity check circuit 210 is a commercially available unit which checks for odd parity over the twelve bits input. If bad parity is detected, parity check circuit 210 provides a logic 0 output on the PEBBTOR lead and also latches the PCM data. This indicates that bad parity was detected on PCM data which is being transmitted to a local RSU subscriber. The processor may then examine the bad parity data.

Parity is also checked on PCM data being transmitted from local RSU subscribers. When PCM data is latched by flip-flop 206, parity check circuit 211 is operated on the P2 lead of that phase of the clock and examines the twelve bits latched by flip-flop array 206. If bad parity is detected, a signal on the PEBRTOB lead has the value of logic 0, indicating that bad parity has been detected on a PCM data sample being transmitted from the originating time switching stage.

Parity check circuits 210 and 211 are connected to alarm read logic 251, which is connected to the processor via four bits of the bi-directional data bus. This informs the processor of the source of any bad parity. In addition, the processor is able to check the alarm read logic 251. Alarm set decode 252 is also connected to the processor via the bi-directional bus. Therefore, the processor is able to set the PEBRTOB and PEBBTOR parity alarm leads to determine the integrity of alarm read logic 251. A logic 1 on bit 0 of the bi-directional data bus indicates that the PEBBTOR signal is to be set and a logic 1 on bit 1 of the bus indicates that the PEBRTOB lead is to be set.

Control decode circuit 253 is connected between the clock and alarm read logic 251. In response to the LBLSSEL and CIOWT signals from the clock control decode circuit 253 generates the OEP signal, which when at logic 0 enables the reading of the parity check circuits 210 and 211 by the processor.

FIG. 5 is a timing diagram of various clock signals produced by the remote clock 12 of the RSU in order to operate the local base link switch 1 as shown above.

It is to be understood that the RSU operation has been shown in simplex form but, with appropriate synchronizing circuitry may be operated as two synchronous duplex copies for reliability.

Although the preferred embodiment of the invention has been illustrated, and that form described in detail, it will be readily apparent to those skilled in the art that various modifications may be made therein without departing from the spirit of the invention or from the scope of the appended claims. 

What is claimed is:
 1. In a remote switching arrangement, a remote switching unit is connected between subscribers and other switching systems via a plurality of interface equipment, said remote switching unit comprising:first and second PCM buses connected to said subscribers and to said other switching systems via said interface equipment for transmitting a plurality of PCM data samples; first and second originating time switching means, each of said originating time switching means being operated to switch said PCM samples from said interface equipment, said first and second originating time switching means being connected to said interface equipment via said first and second buses respectively; each of said originating time switching means including:first and second memory means connected to each of said first and second PCM buses, said first and said second memory means being interconnected so that said first and said second memory means are written into simultaneously corresponding time slots with said transmitted PCM samples; said first and said second memory means further being capable of being operated so that said PCM samples transmitted on said first bus may be switched from said second bus for subsequent retransmission or alternatively said PCM samples transmitted on said second bus may be switched to said first bus for subsequent retransmission; said remote switching unit further comprising:first and second space switching means, said first and second space switching means each including:first latching means connected to said corresponding first and second originating time switching means, said first latching means operated in response to said subsequently transmitted PCM samples to store said PCM sample during each time slot; first multiplexing means connected to said first latching means and operated to transmit said stored PCM samples during each time slot in response to first and second operating signals of first predefined values; and second latching means connected to said multiplexing means and being operated to store said PCM samples transmitted through said multiplexing means during each time slot; said remote switching unit further comprising:first and second terminating time switching means being connected respectively between said first and said second space switching means and said interface equipment, said first and second terminating time switching means respectively operated to switch said PCM samples from said first and second space switching means to said interface equipment for transmission to telephone subscribers; each of said terminating time switching means including:first and second memory means connected between said second latching means and said interface equipment, said first and said second memory means being interconnected so that said first and said second memory means are written into simultaneously in corresponding time slots for storing said PCM samples stored in said second latching means; said first and said second memory means further being capable of being operated to switch said PCM samples from said first space switching means through said second terminating time switching means to said telephone subscribers or alternatively being capable of being operated to switch said PCM samples from said second space switching means through said first terminating time switching means to said telephone subscribers.
 2. A remote switching unit as claimed in claim 1, wherein there is included a clock for producing a plurality of periodic pulses for operating said originating time switching means, said terminating time switching means and said first and second latching means of said space switching means, said clock being connected to said originating time switching means, to said terminating time switching means and to said first and second latching means of said space switching means.
 3. A remote switching unit as claimed in claim 2, wherein there is further included digital tone generation means connected to said originating and said terminating time switching means, said digital tone generation means being operated to generate a plurality of digital tones.
 4. A remote switching unit as claimed in claim 3, wherein there is further included driver/receiver means connected between said space switching means and a second remote switching unit.
 5. A remote switching unit as claimed in claim 4, wherein there is further included processor system means connected to said clock, to said tone generation means, to said driver/receiver means, to said originating and terminating time switching means and to said first and second latching means of said space switching means for controlling said operation of said clock, said tone gneration means, said driver/receiver means, said originating time switching means, said terminating time switching means and first and second latching means of said space switching means.
 6. A remote switching unit as claimed in claim 5, said processor system means including a central processing unit (CPU).
 7. A remote switching unit as claimed in claim 6, said processor system means including bus interface means, said bus interface means being connected between said CPU and said clock, said digital tone generation means, said driver/receiver means, said originating time switching means, said terminating time switching means, and said space switching means.
 8. A remote switching unit as claimed in claim 6, said CPU including a microprocessor.
 9. A remote switching unit as claimed in claim 6, said processor system means further including memory means being operated to store program instruction and data under control of said CPU.
 10. A remote switching unit as claimed in claim 6, said processor system means further including control means connected between said CPU and said second remote switching unit, said control means being operated to monitor data transmitted between a second remote switching unit and said one remote switching units.
 11. A remote switching unit as claimed in claim 6, said processor system means further including a plurality control interface equipment means, each particular control interface equipment means connected to said CPU and to one corresponding interface equipment.
 12. A remote switching unit as claimed in claim 1, wherein each of said first and second memory means of each said originating time switching means includes:a control memory containing switching information for the corresponding originating time switching means; an information memory connected to said corresponding control memory for storing said PCM samples; said information memory of said first memory means connected to said second PCM bus; and said information memory of said second memory means connected to said first PCM bus.
 13. A remote switching unit as claimed in claim 1, wherein each of said first and second memory means of each said terminating time switching means includes:a control memory containing switching information for the corresponding terminating time switching means; an information memory connected to said corresponding control memory for storing said PCM samples; said information memory of said first memory means further connected to said second PCM bus; and said information memory of said second memory means further connected to said first PCM bus.
 14. A remote switching unit as claimed in claim 12, wherein:each information memory of each of said originating time switching means includes at least first and second memory units; said first memory unit of said first memory means is connected to said first memory unit of said second memory means and connected to said first PCM bus; said second memory unit of said first memory means is connected to said second memory unit of said second memory means and connected to said second PCM bus; said first and second memory units of said first memory means are connected to said first space switching means, said first memory unit being operated to transmit said PCM samples to said first space switching means or alternatively said second memory unit being operated to transmit said PCM samples to said first space switching means; and said first and second memory units of said second memory means are connected to said second space switching means, said first memory unit being operated to transmit said PCM samples to said second space switching means or alternatively said second memory unit being operated to transmit said PCM samples to said second space switching means.
 15. A remote switching unit as claimed in claim 13, wherein:each information memory of said terminating time switching means includes at least first and second memory units; said first memory unit of said first memory means is connected to said first memory unit of said second memory means and connected to said first PCM bus; said second memory unit of said first memory means is connected to said second memory unit of said second memory means and connected to said second PCM bus; said first and second memory units of said first memory means are connected to said interface equipment, said first memory unit of said first memory means being operated to transmit said stored PCM samples to said subscriber interface equipment or alternatively said second memory unit of said first memory means being operated to transmit said stored PCM samples to said interface equipment; and said first and second memory units of said second memory means are connected to said interface equipment, said first memory unit of said second memory means being operated to transmit said stored PCM samples to said interface equipment or alternatively said second memory unit of said second memory means being operated to transmit said stored PCM samples to said interface quipment.
 16. A remote switching unit as claimed in claim 15, wherein there is further included:selective attenuation means connected between each of said memory units of said terminating time switching means and said interface equipment, said attenuation means being operated in response to said transmission of said stored PCM samples to selectively alter the amplitude of said PCM samples transmitted to said subscriber interface equipment in response to detection of a predetermined condition of said PCM samples.
 17. A remote switching unit as claimed in claim 16, wherein:said first PCM bus includes:a plurality of connections to said interface equipment; second multiplexing means connected to said interface equipment via said plurality of connections and to said originating time switching means; and first demultiplexing means connected to said selective attenuation means and to said interface equipment via said plurality of connections; and said second PCM bus includes: a plurality of connections to said interface equipment; third multiplexing means connected to said interface equipment via said plurality of connections and to said originating time switching means; second demultiplexing means connected to said selective attenuation means and to said interface equipment via said plurality of connections.
 18. A remote switching unit as claimed in claim 10, wherein there is further included decoding means connected between said CPU, said clock and said first and second space switching means, said decoding means being operated in response to said plurality of periodic pulses to produce a plurality of logic signals for operating said first and second space switching means.
 19. A remote switching unit as claimed in claim 18, each of said space switching means further including selection means connected to said interface equipment, to said clock and to said first multiplexing means, said selection means being operated to transmit said PCM samples from a first interface equipment to said first multiplexing means or alternatively to transmit said PCM samples from a second interface equipment to said first multiplexing means.
 20. A remote switching unit as claimed in claim 19, said selection means of said first space switching means including:fourth multiplexing means connected to said first and second interface equipment and to said clock, said fourth multiplexing means being operated to transmit said PCM samples from said first or alternatively from said second interface equipment; and third latching means connected to said clock, to said fourth multiplexing means and to said first multiplexing means of said first space switching means, said third latching means being operated in response to said fourth multiplexing means to store said PCM samples of said first interface equipment or alternatively said third latching means being operated in response to said fourth multiplexing means to store said PCM samples of said second interface equipment.
 21. A remote switching unit as claimed in claim 19, said selection means of said second space switching means including:fifth multiplexing means connected to a third and a fourth interface equipment and to said clock, said fifth multiplexing means being operated to transmit said PCM samples from said third or alternatively from said fourth interface equipment; and fourth latching means connected to said clock, to said fifth multiplexing means and to said first multiplexing means of said second space switching means, said fourth latching means being operated in response to said fifth multiplexing means to store said PCM samples of said third interface equipment or alternatively said fourth latching means being operated in response to said fifth multiplexing means to store said PCM samples of said fourth interface equipment.
 22. A remote switching unit as claimed in claim 1, wherein there is further included means for generating a predetermined data pattern, said means for generating connected to said first multiplexing means of said first and said second space switching means and said means for generating being operated to produce said predetermined data pattern for each unused time slot.
 23. A remote switching unit as claimed in claim 10, wherein there is further included fifth latching means connected to said clock, to said second remote switching unit and to said first multiplexing means of said first space switching means, said fifth latching means being operated to store said PCM samples transmitted from said second remote switching unit to said one remote switching unit.
 24. A remote switching unit as claimed in claim 10, wherein there is further included sixth latching means connected to said second remote switching unit to said clock and said first multiplexing means of said second space switching means, said sixth latching means being operated to store said PCM samples transmitted from said second remote switching unit to said one remote switching unit.
 25. A remote switching unit as claimed in claim 19, said first space switching means further including seventh latching means connected to said first latching means of said first space switching means, to said first and second interface equipment and to said clock, said seventh latching means being operated to store said PCM samples for transmission to said first and second interface equipment.
 26. A remote switching unit as claimed in claim 21, said second space switching means further including eighth latching means connected to said first latching means of said second space switching means, to said third and fourth interface equipment and to said clock, said eighth latching means being operated to store said PCM samples for transmission to said third and fourth interface equipment.
 27. A remote switching unit as claimed in claim 18, wherein there is further included time slot sequencing means connected to said decoding means, to said CPU, to said clock and to said first multiplexing means of each of said space switching means, said time slot sequencing means being operated to operate said first multiplexing means of each space switching means during each said time slot.
 28. A remote switching unit as claimed in claim 27, said time slot sequencing means including memory means connected to said CPU, to said clock and to said decoding means, said memory means being operated in response to said logic signals to store control data for operating said first multiplexing means of said first and second space switching means during each said time slot.
 29. A remote switching unit as claimed in claim 28, said time slot sequencing means further including ninth latching means connected to said memory means, to said CPU, to said clock and to said first multiplexing means of said first and second space switching means, said ninth latching means being operated to transmit said stored operating signals to said first multiplexing means of each said space switching means and to said CPU.
 30. A remote switching unit as claimed in claim 29, said connection of said ninth latching means to each said first multiplexing means including a two-bit bus for transmitting said operating signals to said first multiplexing means of each said space switching means.
 31. A remote switching unit as claimed in claim 28, wherein said connection of said memory means to said clock and to said CPU includes sixth multiplexing means connected to said memory means, to said clock and to said CPU, said sixth multiplexing means being operated in response to said clock to connect said memory means to said CPU or alternatively to connect said memory means to said clock. 